Processes for the preparation of olefins from oxygenates are known in the art.
U.S. Pat. No. 6,797,851 describes a process for making ethylene and propylene from an oxygenate feed. The process is conducted in two stages using two different zeolite catalysts, wherein in the first stage oxygenates are converted to a light olefin stream, and wherein in the second stage C4+ olefins produced in the first stage are converted to additional ethylene and propylene. The catalyst used for the first stage is a ZSM-5 containing zeolite catalyst. The second stage catalyst is a 10-membered ring zeolite, and ZSM-22, ZSM-23, ZSM-35, ZSM-48 are mentioned. ZSM-35 is preferred. Various embodiments of reaction systems with first and second stage catalyst in separate reaction zones are discussed. Without disclosing an embodiment, it is generally mentioned that the two catalysts can be mixed.
In the known process, significant amounts of aromatics are produced. Most aromatics are produced in the first stage by the conversion of oxygenate over ZSM-5 zeolite, and once formed, aromatics are unlikely to be converted into olefins in the second stage. In Example 2, obtained with ZSM-5 and ZSM-35 the final product after the second stage contains 11 wt % of aromatics.
A positive influence of aromatics in the conversion of methanol or dimethylether to a product containing C2 to C4 olefins olefins is disclosed in U.S. Pat. No. 6,046,372. In the known process, the conversion takes place by contacting a feed containing methanol and/or dimethylether in the presence of an aromatic compound with a catalyst comprising a porous crystalline material, in particular zeolite ZSM-5. In the examples, which were all conducted with ZSM-5, it had been found that the addition of an aromatic compound to the methanol and/or dimethylether feed increased the selectivity of the conversion reaction towards ethylene.
It is desired to provide a process that allows to maximise production of light olefins from an oxygenate feedstock.